1. Field of the Invention
The invention relates to infrared imaging devices and more particularly to a dynamic test system to evaluate their overall performance. The invention is particularly concerned with far-infrared imagers such as the military FLIR device.
2. Description of the Prior Art
The basic element of these devices is a semiconductor photodiode usually made from mercury-cadmium-telluride. These can be made with one diode by using two mirrors to scan the image over the diode, with a line array of diodes and one scanning mirror or better with a two dimensional staring diode array in which every part of the image is being processed at the same time.
Each device has its own unique problems. The single diode is highly dependent on the time response of the diodes. The device using a two dimensional array is highly dependent on the relative responses of the various diodes. The device using the one dimensional array is dependent on both of the above.
A popular test system for these devices includes a thin flat rotating disk separated into angular domains defined by coatings extending between two boundary radii. The coatings alternate between being more or less absorptive and reflective. During the test the disk is rotated at various angular velocities and illuminated with a variable power infrared or far-infrared source. The imaging device is placed to view the disk normally and the relative position of the disk to the device is translated in two directions orthogonal to the disk axis. The resulting electrical signal responses produced by each diode, after amplification and filtering by the device, are then recorded separately. One shortcoming of this type of test is that there is no check of the exit optics or screen unit which is often an integral part of the imaging device. A further shortcoming is the complexity of test data which evolves. When a point in the object space of the imager is near the center of the disc the input varies more rapidly than a similar point near the edge of the disk. As the disk is moved these conditions vary so that a rather complex set of output signals ensue. This places added demands on the computer memory.